This invention relates to an exhaust system for marine engines in more particularly to an improved exhaust system that does not adversely affect high range performance and, at the same time, provides good silencing at low engine speeds.
It is well known that water cooled marine engines, be they either inboard drives or outboard drives, including outboard motors, generally mix the engine coolant discharged from the cooling jacket with the exhaust gases prior to discharge to the atmosphere either directly or back through the body of water in which the watercraft is operating. With regard to such systems, the introduction of the coolant into the exhaust system simplifies the plumbing associated with the engine and also provides some significant silencing and cooling of the exhaust gases. However, the introduction of the water into the exhaust system can give rise to back pressure in the exhaust system that adversely affects the high range performance.
Therefore, systems have been proposed which include water separators which will separate the engine coolant from the exhaust gases and which discharge the coolant through a separate discharge from the exhaust discharge. The systems provide either centrifugal or gravitational separation and provide this degree of separation independent of engine speed. These arrangements, therefore, have a tendency to cause substantial noise through exhaust gas discharge through the water outlet under slow speed running which is not satisfactory.
It is, therefore, a principle object of this invention to provide an exhaust system for a marine engine wherein silencing is achieved at low speeds and wherein it is insured that good water separation is achieved at high speeds so as to reduce back pressure and improve engine performance.
It is a further object of this invention to provide an improved exhaust system for a marine engine wherein water separation is achieved primarily only at the higher engine speeds so as to avoid noise at low speeds and improve high speed performance.